1. Field of the Invention
The present invention relates to radios for use in vehicles, and, more particularly, to sensitivity settings in radios for use in vehicles.
2. Description of the Related Art
With car radios becoming more widely dispersed around the world, it is becoming more advantageous for the radios to detect characteristics of their environment and adjust internal settings of the radios accordingly. Currently most digital AM/FM tuners utilize a fixed tuner sensitivity threshold for the Tuner Auto Seek operation, i.e., the operation wherein the tuner automatically scans across a frequency band until it comes to, and stops at, a frequency having a sufficiently strong signal. Most digital AM/FM tuners also utilize fixed parameters for other functions. The use of fixed tuner sensitivity thresholds and fixed parameters may result in audio quality that is uneven under different signal conditions. The fixed threshold and parameters values are typically defined within the calibration data according to region.
In the case of the tuner sensitivity threshold, while a lower threshold value may enable the radio to better differentiate between noise and a valid station, the use of a fixed higher level threshold may limit the ability of the radio to identify valid stations via the Auto Seek operation as the driver travels from an urban to a suburban or rural surrounding environment. The lowered ability to identify valid stations via the Tuner Seek operation could arise because, in the suburban or rural environment, the radio may receive only lower signal levels that are below the actual threshold that is set for the upper limit.
Some of the other functions for which most digital AM/FM tuners utilize fixed parameters include Soft Mute, High Cut, and Stereo Blend. Soft Mute may be used in low signal sensitivity conditions to mute the audio in order to prevent static noise from disturbing the listening comfort of the end user. High Cut likewise defines the clamping down of high frequencies in cases where signal strength, multipath or adjacent channel is beyond a specified level. Stereo Blend also enhances the overall listening experience of the user in harsh environments by blending the stereo signal to a mono signal, and converting the signal back from mono to stereo when the signal conditions get better.
In the operation of a digital signal processor (DSP), an “attack time” may define the rate at which bandwidth increases, and “release time” may define the rate at which bandwidth shrinks. Conventional AM/FM tuners set fixed attack and release times for the Soft Mute, Stereo Blend and High Cut features. However, the attack time and release time for Stereo Blend, for example, that are optimized for high sensitivity regions might not work well for low sensitivity regions.
A radio convention or standard that differs between regions of the world is the use of Radio Data System (RDS) and Radio Broadcast Data System (RBDS). RDS is a standard from the European Broadcasting Union for sending small amounts of digital information using conventional FM radio broadcasts. The RDS system standardizes the transmission format of several types of information, such as the time of day and identification of the track, artist and radio station. RBDS is the United States version of RDS. With regard to RDS/RBDS sensitivity, the radio typically requires a certain field strength sensitivity before RDS/RBDS synchronization can be achieved in order to receive Program Identification Code, Program Service Name, Alternate Frequency List and others which are defined in the RDS/RBDS standard protocol. The sensitivity may have dependencies on characteristics of the wireless environment including front-end filter bandwidth, field strength, multipath and adjacent channel interference to which the currently listened-to station is subjected.
Conventional automotive radio head units store two Tuner Seek sensitivity threshold settings, namely, the Local and DX threshold settings, for the Tuner Auto Seek operation within calibration data. A local Seek operation typically maintains a higher threshold and, during triggering of Seek, the first pass utilizing this higher threshold may try to find station signals that meet or exceed this threshold level. If a signal exceeding the threshold level cannot be found after completing one pass across the entire spectrum range (87.7 MHz to 107.9 MHz in the U.S.) with the Local threshold, a DX threshold, which is lower than the Local threshold, may be utilized to find stations whose signal exceeds the lower DX threshold.
Due to the need to scan first with the Local threshold and scan again with the DX threshold, conventional radios typically require two passes in low sensitivity areas in order to find a station that meets the DX threshold in the event that no station exists that meets the Local threshold. In rural areas, these two scans require the user to wait for up to sixteen seconds assuming that seek speed is 75 milliseconds per station. That is, the U.S. FM band has 102 frequencies, and spending 75 milliseconds on each of these frequencies requires about eight seconds in order to complete one scan.
Accordingly, what is neither anticipated nor obvious in view of the prior art is a method of setting threshold values while in a non-tuner mode of operation, and without having to make two separate scans of the frequency spectrum. What is also neither anticipated nor obvious in view of the prior art is any means to adaptively increase the gain on the IF signal, alter the front end bandwidth bounds, and adjust the high cut filter bandwidth.